A relationship between the indirect human consumption of milk products derived from bracken fern fed cows will be sought. Cows and rats are highly susceptible to urinary bladder carcinogenesis by bracken fern. Milk obtained from cows ingesting bracken fern contains at least two chemicals not normally present in cows milk. Humans ingesting such milk might be unwittingly exposed to a naturally occurring plant carcinogen. Milk and urine obtained from bracken fern fed cows will be tested in rodents for carcinogenic activity. A search for bladder carcinogens in these fluids will be conducted utilizing animal and microbiological assay systems. A definition of the characteristics of latent period, growth rate, and bladder tumor incidence in rats ingesting bracken fern will be obtained. The proposed studies are designed to meet the specific study objectives outlined in the Experimental Biology Subflow Phase II-1.1-A, Phase II-2.1-A, and Phase II-2.2-B of the National Bladder Cancer Project.